This invention relates to a noise canceling handset, particularly, relates to a noise canceling microphone unit that is used for composing a noise canceling handset by the use of a normal housing for a normal handset.
A conventional telephone set has a handset. The handset comprises a closed housing which usually composed of an upper case and a lower case assembled to each other to define a closed space therein. The closed space has a microphone receiving space portion and an earphone receiving space potions. The closed housing or the lower case has a mouthpiece surface at a portion corresponding to the microphone receiving space portion. A user speaks his message towards the mouthpiece surface through which the speech sound is transmitted to the microphone mounted in the microphone receiving space portion. Therefore, the microphone surface has usually vent holes for permitting the sound to transfer through the mouthpiece surface. Therefore, not only the speech sound but also surrounding sound transfer through the mouthpiece surface to reach the microphone.
In some handsets, speech can be picked up with surrounding noises being canceled. Such handsets are called noise canceling handsets.
A conventional noise canceling handset comprises a noise canceling microphone element that has first and second acousto-electric transducers (i.e. microphones) fixed to each other back to back. That is, the noise canceling microphone element has first and second sound sensing surfaces at the opposite ends. The acousto-electric transducers are, for example, condenser microphones. Different sounds incoming to the first and second sensing surfaces are converted into electric signals by the two acousto-electric transducers, respectively. Those electric signals are subtracted to each other to form a resultant electric signal, which represents a sound pressure difference between sounds sensed at the first and the second sound sensing surfaces. The resultant electric signal represents the speech directed to the mouthpiece surface but without the surrounding noise, because the surrounding noise is cancelled since it is sensed at both of the first and second sensing surfaces.
However, the closed housing of the handset used for containing the noise canceling microphone element has a special structure where the closed housing has a side surface directing in a direction different from the mouthpiece surface. The first acousto-electric transducer and the second acousto-electric transducer are mounted in the closed housing to face the mouthpiece surface and the side surface, respectively. With this structure, the surrounding noises are sensed by both of the first and the second acousto-electric transducers and the voice is mainly sensed by the first acousto-electric transducer.
The first and the second acousto-electric transducers are actuated by sound waves and produce essentially equivalent electric waves as first and second signals, respectively. The noise canceling microphone element produces an electric difference signal representative of a difference between the first signal and the second signal. As mentioned above, the first and the second acousto-electric transducers similarly pick up surrounding noises and the first acousto-electric transducer further picks up the voice while the second acousto-electric transducer hardly picks up the voice. Accordingly, the difference signal produced by the noise canceling microphone element substantially represents the voice without noises.
By the way, it is necessary for manufacture of the special housing to use special metallic molds. That is why the special housing has an opening in the side surface and has a vent tube from the opening to the second acousto-electric transducer. The vent tube leads the noises to the second transducer and prevents sound from reaching from an earphone through the housing.
Therefore, the special metallic molds are necessary to manufacture the special housing of the noise canceling handset. This means that big investment in plant and equipment is necessary when manufacture of the noise-canceling handset is started.
It is therefore an object of this invention to provide a noise canceling microphone unit for composing a noise canceling handset by the use of a normal housing for a normal handset.
It is another object of this invention to provide a microphone holder for substituting a normal housing of a normal handset for a special housing of a noise canceling handset.
It is still another object of this invention to provide a noise canceling handset which has a normal housing for a normal handset.
It is yet another object of this invention to provide a noise canceling handset which is inexpensive.
It is further still another object of this invention to provide a method of mounting a noise canceling microphone in a normal housing for a normal handset.
Other object of this invention will become clear as the description proceeds.
According to a first gist of this invention, a noise canceling microphone unit is for use in a handset having a closed housing defining a microphone receiving space therein. The housing has a mouthpiece surface and a side surface. The noise canceling microphone unit is mounted in the microphone receiving space and comprises a noise canceling microphone element having first and second sound sensing surfaces at opposite ends thereof to produce an electric signal representing a sound difference between a first sound sensed at the first sound sensing surface and a second sound sensed at the second sound sensing surface. A microphone holder fixedly holds the noise canceling microphone element therein. The microphone holder comprises a hollow cylinder having opposite first and second open ends. The first open end faces the mouthpiece surface when the microphone holder is mounted in the microphone receiving space. The hollow cylinder fixedly holds therein the noise canceling microphone element with the first sound sensing surface being directed to but short of the first open end while the second sound sensing surface directed to but short of the second open end. A vent tube laterally extends from the hollow cylinder and opens in the hollow cylinder at a position between the second open end and the second sound sensing surface of the noise canceling microphone element held in the hollow cylinder. The vent tube has an extending open end. The extending open end is opened to the outside of the housing through the side surface when the microphone holder is mounted in the microphone receiving space. A circuit board is connected to the noise canceling microphone element and mounted on the hollow cylinder to close the second open end.
According to a second gist of this invention, a microphone holder is for use in a handset to hold a noise canceling microphone element having a microphone length. The microphone holder comprises a hollow cylinder which has a peripheral surface between a first open end and a second open end and a cylinder length longer than the microphone length for defining an inner space to receive the noise canceling microphone. A vent tube is formed on the peripheral surface at a position which is nearer to the second open end than the noise canceling microphone received in the inner space. The vent tube extends outward to an extending open end and defines a passage which leads form the extending open end to the inner space.
According to a third gist of this invention, a microphone holder fixedly holds a noise canceling microphone element in a handset having a closed housing defining a microphone receiving space therein. The housing has a mouthpiece surface and a side surface. The noise canceling microphone element has first and second sound sensing surfaces at opposite ends thereof to produce an electric signal representing a sound difference between a first sound sensed at said first sound sensing surface and a second sound sensed at said second sound sensing surface. The microphone holder comprises a hollow cylinder having opposite first and second open ends. The first open end faces the mouthpiece surface when the microphone holder is mounted in the microphone receiving space. The hollow cylinder fixedly holds therein the noise canceling microphone element with the first sound sensing surface being directed to but short of the first open end while the second sound sensing surface directed to but short of said second open end. A vent tube laterally extends from the hollow cylinder and opens in the hollow cylinder at a position between the second open end and the second sound sensing surface when the noise canceling microphone element is held in the hollow cylinder. The vent tube has an extending open end so that the extending open end is opened to the outside of the housing through the side surface when the microphone holder is mounted in the microphone receiving space.
According to a fourth gist of this invention, a noise canceling handset includes a noise canceling microphone element having a microphone length. The noise canceling handset comprises a microphone holder for holding the noise canceling microphone element. The microphone holder comprises a hollow cylinder having a peripheral surface between a first open end and a second open end and a cylinder length longer than the microphone length for defining an inner space to receive the noise canceling microphone element. A vent tube is formed on the peripheral surface at a position which is nearer to the second open end than the noise canceling microphone received in the inner space. The vent tube extends outward to an extending open end and defining a passage which leads from the extending open end to the inner pace. A housing has a mouthpiece surface and a side surface for defining a microphone receiving space to receive the noise canceling microphone element held by the microphone holder. The microphone holder is fixed to the housing at the microphone receiving space so that the first open end faces said mouthpiece surface and that said extending open end is opened to the outside of said housing through said side surface.
According to a fifth gist of this invention, a noise canceling handset has a closed housing defining a microphone receiving space therein. The housing has a mouthpiece surface and a side surface. The noise canceling handset comprises a noise canceling microphone element having first and second sound sensing surfaces at opposite ends thereof to produce an electric signal representing a sound difference between a first sound sensed at the first sound sensing surface and a second sound sensed at the second sound sensing surface. A microphone holder fixedly holds the noise canceling microphone element therein. The microphone holder is mounted in the microphone receiving space and comprises a hollow cylinder having opposite first and second open ends. The first open end faces the mouthpiece when the microphone holder is mounted in the microphone receiving space. The hollow cylinder fixedly holds therein the noise canceling microphone element with said first sound sensing surface being directed to but short of said first open end while said second sound sensing surface directed to but short of the second open end. A vent tube laterally extends from the hollow cylinder and opens in the hollow cylinder at a position between the second open end and the second sound sensing surface of the noise canceling microphone element held in the hollow cylinder. The vent tube has an extending open end. The extending open end is opened to the outside of said housing through the side surface when the microphone holder is mounted in the microphone receiving space. A circuit board is connected to the noise canceling microphone element and mounted on the hollow cylinder to close the second open end.
According to a sixth gist of this invention, a method of mounting a noise canceling microphone element in a microphone receiving space defined by a closed housing of a handset is provided. The noise canceling microphone element has first and second sound sensing surfaces at opposite ends thereof to produce an electric signal representing a sound difference between a first sound sensed at the first sound sensing surface and a second sound sensed at the second sound sensing surface. The housing has a lower member with a mouthpiece surface and an upper member with a side surface. The method comprises the steps of preparing a microphone holder for fixedly holding said noise canceling microphone element therein. The microphone holder comprises a hollow cylinder having opposite first and second open ends for fixedly holding therein the noise canceling microphone element. A vent tube laterally extends from the hollow cylinder and opening in the hollow cylinder at a position between the second open end and the second sound sensing surface when the noise canceling microphone element is held in the hollow cylinder. The vent tube has an extending open end so that the extending open end is opened to the outside of the housing through the side surface when the microphone holder is mounted in the microphone receiving space. The method further comprises the steps of holding the noise canceling microphone element in the microphone holder with the first sound sensing surface being directed to but short of the first open end while the second sound sensing surface directed to but short of the second open end so that a circuit board connected to said noise canceling microphone element is mounted on said hollow cylinder and closes the second open end, mounting the microphone holder together with the noise canceling microphone held by the microphone holder in the microphone receiving space on side of the lower member so that the first open end faces the mouthpiece when the microphone holder is mounted in the microphone receiving space, fixing the microphone holder together with the circuit board to the lower member, making an opening in the side surface so as to correspond to the extending open end of the vent tube of the microphone holder fixed to the lower member, and combining the upper member with the lower member so that the extending opening end is inserted into the opening.